Various articles of footwear structures are known for use during cold weather conditions and most of these consists in the insulation of the upper of the article of footwear. The sole structure usually consists of a solid structure and an insulating insole, such as “THINSULATE”™(fiber insulation), a registered trademark of the 3M Corporation, is disposed thereover inside the article of footwear for use as a barrier between the cold sole and the wearer's feet. This provides minimal resistance against the transfer of the cold emanating from the ground through the sole and to the feet of the wearer person. It is known that a major part of cold feet is caused by the sole of the article of footwear which is not capable of resisting to the cold emanating from the ground and thereby resulting in major heat loss incurring from the wearer's feet. The risk of frostbite on any exposed skin can have a lasting effect on the sensory nerves of the foot, especially the toes. Keeping a thermal buffer between one's foot and the frozen ground is very important as a significant amount of body heat can be lost through one's feet. It would therefore be desirable to create soles that are more thermally efficient to buffer the cold emanating from the ground and provide the wearer person comfort to its feet while maintaining breathability and comfort during cold weather conditions.
It is known that the sole of a shoe deforms less during cold weather conditions due to an increase in stiffness resulting in that a smaller area of a wearer's foot is in contact with the shoe insole during impact of the sole of the shoe with the ground surface. This results in more localized pressure on the foot and putting more pressure or impact force on a smaller area of the foot, much like running on a hard surface. It would therefore be desirable to construct an article of footwear with a sole providing more flexibility, better impact absorbing, lightweight and better insulation properties during cold weather conditions.
Down insulation from duck and goose feathers is known as an excellent insulator due to its superior heat retaining properties. However, down is difficult to handle during manufacturing of products containing down. My U.S. Pat. No. 6,025,041 addresses this problem and resolves it by the construction of down feather sheets in which the down is held captive in a substantially evenly distributed form. It would therefore also be desirable to use down in the construction of the sole of article of footwear to provide insulation therein.